“Reducing fevers raises spread of flu” was one of the headlines describing a Canadian study on the effects of fever-reducing painkillers on the potential spread of the influenza virus.
Using computer modelling, the authors suggested that fever suppression increases the flu transmission rate in a population. This work was based on two assumptions: first, that suppressing fever will cause an individual to get out of bed and interact with others while still infectious, and secondly, as lead researcher David Earn, put it, “…fever can actually help lower the amount of virus in a sick person’s body...”
There is a lot of evidence supporting the latter point, and this research from McMaster University Ontario opened another chapter in the debate over whether we should treat fever or not.
Fever: Therapeutic Tool or Dangerous Symptom?
Fever is the body’s response to infection, and is normally self-resolving and harmless. In fact, a century ago, doctors viewed fever as a therapeutic tool. Neurosyphilis – at the time an untreatable condition – was cured with a malaria-induced fever, a technique known as pyrotherapy. Patients were subsequently given quinine to cure the malaria.
Now, however, the attitude towards fever has changed and the standard advice is to alleviate it, often with fever-reducing drugs known as antipyretics. Paracetamol (acetaminophen) and ibuprofen are two of the most commonly used antipyretics which also act as painkillers.
Their use is particularly widespread for treating children, for whom fever can be distressing. As the use of antipyretic painkillers for fever increases, the question of whether antipyretics prolong the underlying illness becomes more pertinent.
Antipyretics can be Bad for Recovery
An increasingly popular view is that fever may be an adaptive response, evolved to help fight an infection. A review of published studies on this subject found that reducing fever (either by antipyretics or physical cooling) does not reduce the duration of an illness – but can instead prolong it. The idea that elevating body temperature is beneficial is supported by studies on animals. Rodents that are housed at elevated temperatures recover more quickly from bacterial infection or septic shock. In ferrets, fever suppression increases flu virus shedding and duration.
Fever Speeds Recovery? How Could This Work?
There are two ways in which fever may speed recovery from illness: by boosting the immune response to the infection; or by directly blocking replication of the micro-organism.
For the first mechanism, there is evidence that fever-range (febrile) temperatures enhance many aspects of the host immune response. T cell proliferation and cytotoxic activity, neutrophil and dendritic cell migration, according to the work of Fisher in 2010, and the release of active pro-inflammatory cytokines can all be increased at febrile temperatures.
The evidence for killing or reduction of microbe levels being directly attributed to fever is less clear. Some older studies have shown that bacteria are more susceptible to antibiotics at febrile temperatures, but the elevated temperature alone is insufficient to kill.
Research: Does Fever Fight Infection?
While in vitro experiments are informative in terms of how fever may help fight infection, the ultimate test of whether and how well it does so must come from clinical studies. Experiments of the sort done by Nobel prize winner Julius Wagner-Jauregg, involving infecting patients with malaria, could never be done today.
Instead, researchers conducted a particularly well-cited study from 1990 to look at the effects of over-the-counter drugs on the progression of the common cold, a rhinovirus infection. Aspirin and paracetamol increased symptoms, suppressed the antibody response, and prolonged virus shedding. More recently, a study on children receiving vaccinations found that acetaminophen reduced the antibody responses to all vaccines.
Fever Reduction Studies: Inconclusive
Data suggesting fever reduction slows recovery is balanced by studies showing no difference. A recent meta-analysis of investigations into the effect of antipyretics on acute illnesses in children, found no effect on recovery from illness. The argument for reducing fever is also stronger in certain types of patients such as the critically ill (for whom the elevated heart rate associated with fever can be dangerous), the very old and children.
There is a need for large-scale randomised controlled trials to provide better clinical data on the effects of fever on illness. However, investigating the possible benefits of not taking drugs is unlikely to be something large pharmaceutical companies will invest in.